Refrigeration cycle apparatus

ABSTRACT

In a refrigeration cycle apparatus in which carbon dioxide is used as refrigerant and refractory oil is used as lubricating oil in a compressor, it is an object of the present invention to reduce influence of adhesion of lubricating oil to the internal heat exchanger, and to enhance the heat exchanging efficiency of the internal heat exchanger.  
     A refrigeration cycle apparatus in which a compressor  11 , a radiator  12 , an expansion valve  13  and an evaporator  14  are connected to one another through tubes, said refrigeration cycle apparatus comprises an internal heat exchanger  30  for exchanging heat between a high pressure refrigerant which flows out from said radiator  12  and low pressure refrigerant which flows out from said evaporator  14 , wherein carbon dioxide is used as the refrigerant, refractory oil is used as lubricating oil in said compressor  11 , said internal heat exchanger  30  comprises a first heat exchanger tube  31  through which the high pressure refrigerant in a supercritical region flows and a second heat exchanger tube  32  through which the low pressure refrigerant flows, said first heat exchanger tube  31  is disposed in said second heat exchanger tube  32.

TECHNICAL FIELD

The present invention relates to a refrigeration cycle apparatus in which a compressor, a radiator, an expansion valve and an evaporator are connected to one another through tubes, said refrigeration cycle apparatus comprises an internal heat exchanger for exchanging heat between a high pressure refrigerant which flows out from said radiator and a low pressure refrigerant which flows out from said evaporator.

BACKGROUND TECHNIQUE

As a refrigeration cycle apparatus in which load against environment is small, a high amount of heat can be taken out, refrigeration oil returns to the compressor excellently, and the refrigeration cycle apparatus can be used stably for the long term, there is proposed a refrigeration cycle apparatus which uses carbon dioxide as refrigerant and uses non-compatible type or difficult-compatible type lubricating oil as refrigeration oil (e.g., see patent document 1).

There is proposed an internal heat exchanger used as a refrigeration cycle apparatus which uses carbon dioxide as refrigerant, and the internal heat exchanger has a simple structure and high heat exchanging ability (e.g., see patent document 2).

According to the internal heat exchanger of the patent document 2, an intermediate-diameter tube is concentrically disposed in a large-diameter tube, refrigerant of low temperature and low pressure refrigerant flows through the intermediate-diameter tube, and high temperature and high pressure refrigerant flows between the large-diameter tube and the intermediate-diameter tube. In the patent document 2, the high temperature and high pressure refrigerant is disposed on the outer peripheral side of the internal heat exchanger. With this, the high temperature and high pressure refrigerant is allowed to exchange heat with outside air, thereby increasing the heat release amount.

[Patent Document 1] Japanese Patent Application Laid-open No. 2001-255030 (see paragraphs (0016) and (0017))

[Patent Document 2] Japanese Patent Application Laid-open No. 2001-56188 (see paragraphs (0043) and (0049))

DISCLOSURE OF THE INVENTION

[Problem to be Solved by the Invention]

In the refrigeration cycle apparatus using carbon dioxide as refrigerant, it is effective to use the internal heat exchanger for enhancing COP.

In the refrigeration cycle apparatus having the internal heat exchanger, however, if low compatible lubricating oil is used as lubricating oil in the compressor like the patent document 1, refrigerant and lubricating oil are separated from each other especially in a low pressure region and thus, there is a problem that lubricating oil remains in a low pressure side tube of the internal heat exchanger.

On the other hand, if a so-called double tube is used like the patent document 2, an internal heat exchanger having a simple structure can be realized, but if low compatible lubricating oil is used as lubricating oil in the compressor, if lubricating oil adheres to a heat transfer surface between the high temperature and high pressure refrigerant and the low temperature and low pressure refrigerant, there is a problem that heat exchanging efficiency is deteriorated.

Hence, in a refrigeration cycle apparatus in which carbon dioxide is used as refrigerant and refractory oil is used as lubricating oil in a compressor, it is an object of the present invention to reduce influence of adhesion of lubricating oil to the internal heat exchanger, and to enhance the heat exchanging efficiency of the internal heat exchanger.

[Means for Solving Problems]

A first aspect of the present invention provides a refrigeration cycle apparatus in which a compressor, a radiator, an expansion valve and an evaporator are connected to one another through tubes, the refrigeration cycle apparatus comprises an internal heat exchanger for exchanging heat between a high pressure refrigerant which flows out from the radiator and a low pressure refrigerant which flows out from the evaporator, wherein carbon dioxide is used as the refrigerant, refractory oil is used as lubricating oil in the compressor, the internal heat exchanger comprises a first heat exchanger tube through which the high pressure refrigerant in a supercritical region flows and a second heat exchanger tube through which the low pressure refrigerant flows, and the first heat exchanger tube is disposed in the second heat exchanger tube.

According to a second aspect of the invention, in the refrigeration cycle apparatus of the first aspect, the number of first heat exchanger tube is two or more.

According to a third aspect of the invention, in the refrigeration cycle apparatus of the first aspect, a straight tube having a smooth outer surface is used as the first heat exchanger tube, and only the first heat exchanger tube is disposed in the second heat exchanger tube.

According to a fourth aspect of the invention, in the refrigeration cycle apparatus of the first aspect, the internal heat exchanger is provided at its opposite ends with connection tubes each having predetermined length, one end side opening of each of the connection tubes is formed smaller than the other end side opening by diameter-increasing machining or diameter-reducing machining, the second heat exchanger tube is connected to the one end side opening, the first heat exchanger tube is connected to the other end side opening, and a tube through which the low pressure refrigerant flows is connected to the other end side opening.

According to a fifth aspect of the invention, in the refrigeration cycle apparatus of the first aspect, a flow path cross-sectional area of the low pressure refrigerant formed by the first heat exchanger tube and the second heat exchanger tube is equal to or greater than an inner diameter cross-sectional area of an outlet-side tube of the evaporator.

[Effect of the Invention]

According to the present invention, it is possible to reduce influence of adhesion of lubricating oil to the internal heat exchanger, and to enhance the heat exchanging efficiency of the internal heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a heat pump water heater according to an embodiment;

FIG. 2 is a diagram showing two phase separation temperature of CO₂ refrigerant and various oils of the embodiment;

FIG. 3 is a side view of an essential portion of the internal heat exchanger of the embodiment;

FIG. 4 is a sectional view taken along the like X-X in FIG. 3;

FIG. 5 is a sectional view taken along the like Y-Y in FIG. 3;

FIG. 6 is a side view of an essential portion of an internal heat exchanger of an other embodiment of the invention; and

FIG. 7 is a sectional view taken along the like Z-Z in FIG. 6.

EXPLANATION OF SYMBOLS

-   11 compressor -   12 radiator -   13 expansion valve -   14 evaporator -   15 high pressure-side tube -   16 low pressure-side tube -   31 first heat exchanger tube -   32 second heat exchanger tube -   33 connection tube

BEST MODE FOR CARRYING OUT THE INVENTION

According to the refrigeration cycle apparatus of the first aspect of the invention, carbon dioxide is used as the refrigerant, refractory oil is used as lubricating oil in the compressor, the internal heat exchanger comprises a first heat exchanger tube through which the high pressure refrigerant in a supercritical region flows and a second heat exchanger tube through which the low pressure refrigerant flows, and the first heat exchanger tube is disposed in the second heat exchanger tube. With this aspect, the first heat exchanger tube is disposed in the second heat exchanger tube, and low pressure refrigerant flows through the second heat exchanger tube. With this, as compared with a case in which low pressure refrigerant flows through the first heat exchanger tube, the contact area with respect to the heat exchanger tube of lubricating oil and thus, film thickness of lubricating oil on a heat exchanger tube surface can be reduced, and heat exchanging efficiency in the internal heat exchanger is enhanced.

According to the second aspect of the invention, in the refrigeration cycle apparatus of the first aspect, the number of first heat exchanger tube is two or more. With this aspect, since the number of first heat exchanger tube is two or more, the contact area with respect to the heat exchanger tube of lubricating oil can further be increased and thus, the film thickness of lubricating oil on the heat exchanger tube surface can further be reduced, and the heat exchanging efficiency in the internal heat exchanger is enhanced.

According to a third aspect of the invention, in the refrigeration cycle apparatus of the first aspect, a straight tube having a smooth outer surface is used as the first heat exchanger tube, and only the first heat exchanger tube is disposed in the second heat exchanger tube. With this aspect, the outer surface of the first heat exchanger tube is smoothened, and a support member of the first heat exchanger tube with respect to the second heat exchanger tube is not provided between the first heat exchanger tube and the second heat exchanger tube. Therefore, lubricating oil flows smoothly, and an amount of lubricating oil remaining in the internal heat exchanger can be reduced, and the heat exchanging efficiency in the internal heat exchanger is enhanced.

According to a fourth aspect of the invention, in the refrigeration cycle apparatus of the first aspect, the internal heat exchanger is provided at its opposite ends with connection tubes each having predetermined length, one end side opening of each of the connection tubes is formed smaller than the other end side opening by diameter-increasing machining or diameter-reducing machining, the second heat exchanger tube is connected to the one end side opening, the first heat exchanger tube is connected to the other end side opening, and a tube through which the low pressure refrigerant flows is connected to the other end side opening. With this aspect, using the connection tube having the predetermined length, the first heat exchanger tube is connected to one of the openings, the tube through which low pressure refrigerant flows is connected also to the opening, the high pressure refrigerant and the low pressure refrigerant flows from the same opening at the branch. With this, lubricating oil can smoothly flow through the inflow portion and outflow portion of the internal heat exchanger. Therefore, the amount of lubricating oil remaining in the internal heat exchanger can be reduced, and the heat exchanging efficiency in the internal heat exchanger can be enhanced.

According to a fifth aspect of the invention, in the refrigeration cycle apparatus of the first aspect, a flow path cross-sectional area of the low pressure refrigerant formed by the first heat exchanger tube and the second heat exchanger tube is equal to or greater than an inner diameter cross-sectional area of an outlet-side tube of the evaporator. With this aspect, lubricating oil can smoothly flow through the internal heat exchanger and thus, the amount of lubricating oil remaining in the internal heat exchanger can be reduced, and the heat exchanging efficiency in the internal heat exchanger can be enhanced.

EMBODIMENT 1

An embodiment of the present invention will be explained based on a heat pump water heater according to an embodiment of the invention will be explained.

FIG. 1 is a circuit diagram of the heat pump water heater of the embodiment of the invention.

The heat pump water heater of the embodiment comprises a refrigeration cycle apparatus 10 and a hot water storing apparatus 20.

The refrigeration cycle apparatus 10 comprises a refrigeration cycle in which a compressor 11, a radiator 12, an expansion valve 13 and an evaporator 14 are connected to one another through tubes. The internal heat exchanger 30 exchanges heat between high pressure refrigerant flowing through a high pressure-side tube 15 extending from the radiator 12 to the expansion valve 13 and low pressure refrigerant flowing through a low pressure-side tube 16 extending from the evaporator 14 to the compressor 11. The radiator 12 exchanges heat between high pressure refrigerant discharged from the compressor 11 and stored hot water supplied from the hot water storing apparatus 20. In the radiator 12, a flowing direction of refrigerant and a flowing direction of the stored hot water is opposite from each other.

A vaporizing fan 17 is a blower for sending air to the evaporator 14. A water tube 18 introduces stored hot water to the radiator 12, and discharges hot water heated by the radiator 12.

The compressor 11, the expansion valve 13 and the internal heat exchanger 30 are disposed in a compressor-side casing 10A of the refrigeration cycle apparatus 10. The radiator 12, the evaporator 14 and a vaporizing fan 17 are disposed in a wind passage-side casing 10B of the refrigeration cycle apparatus 10. The compressor-side casing 10A and the wind passage-side casing 10B are divided from each other. It is preferable that the internal heat exchanger 30 is close to the compressor 11.

The refrigeration cycle apparatus 10 uses carbon dioxide as refrigerant, and is driven in a state exceeding critical pressure on the high pressure side. Refractory oil is used as lubricating oil in the compressor 11. Lubricating oil having viscosity of 5 to 300 cSt at 40° C. is suitable as the refractory oil of the invention. The refractory oil of the invention has a region of oil rate at which the oil is not compatible in a range of −40° C. to 31° C. Here, compatible, non-compatible and difficult-compatible of oil will be explained in detail based on FIG. 2.

FIG. 2 shows two phase separation temperature of CO₂ refrigerant and various oils. In PVE (polyvinyl ether), POE (polyol ester) and PC (polycarbonate), a region of oil rate in which oil is not compatible at −40° C. to 31° C. is only a portion of the region at relatively high temperature. In the case of PC for example, there exists a region of non-compatible oil rate at equal to or more than 5° C. Thus, these oils are compatible oil.

On the other hand, PAO (polyalpha olefin, AB (alkylbenzene) and M (mineral oil) have regions of non-compatible oil rate in a range of −40° C. to 31° C. These oils are low compatible non-compatible oil.

Further, PAG (polyalkylene glycol) has a region of non-compatible oil rate in a range of −40° C. to 31° C. but since CO₂ of 45 to 75% is dissolved also in oil rich phase, this oil has low compatible as compared with compatible oil such as PVE, POE and PC, but this oil is difficult-compatible oil having high compatibility as compared with non-compatible oil such as PAO, AB and mineral oil.

Here, as refractory oil, non-compatible type lubricating oil such as mineral oil, PAO (polyalpha olefin) and alkylbenzene are included, and difficult-compatible type lubricating oil such as PAG (polyalkylene glycol) is preferable.

The hot water storing apparatus 20 includes a hot water storing tank 21. A bottom tube 22 of the hot water storing tank 21 is connected to a water supply pipe such as a tap water pipe through a flow rate adjusting valve, a pressure-reducing valve and a check valve. A bottom outflow tube 23 is connected to a inflow side connection opening of the water tube 18 through a circulation pump 24. An upper circulation tube 25 of the hot water storing tank 21 is connected to an outflow side connection opening of the water tube 18. A supply tube 26 is connected to an upper portion of the hot water storing tank 21. The hot water storing tank 21 of the embodiment is a laminated type hot water storing tank, stirring operation in the tank is prohibited, high temperature water is stored in the upper portion and low temperature water is stored in the bottom.

Next, water heater storing operation of the heat pump water heater according to the embodiment will be explained.

If the refrigeration cycle apparatus 10 detects that an amount of hot water in the hot water storing tank 21 becomes equal to or less than a predetermined amount, the refrigeration cycle apparatus 10 starts operating.

Refrigerant is compressed to supercritical region by the compressor 11, the refrigerant dissipates heat to the radiator 12 and the internal heat exchanger 30 and then, the refrigerant is decompressed by the expansion valve 13, absorbs heat at the evaporator 14 and the internal heat exchanger 30, and the refrigerant is sucked into the compressor 11 in its gaseous state.

As soon as the compressor 11 is operated, the operation of the pump 24 of the water heater 20 is also started. By operating the pump 24, cool water in the bottom of the hot water storing tank 21 is introduced into the water tube 18 from the bottom outflow tube 23, the water is heated by the radiator 12 and the hot water is introduced into the upper portion of the hot water storing tank 21 from the water tube 18 through the upper circulation tube 25.

If a predetermined amount of hot water is stored in the hot water storing tank 21, the operations of the compressor 11 and the pump 24 are stopped.

Next, the internal heat exchanger used for the heat pump water heater of the embodiment will be explained.

FIG. 3 is a side view of an essential portion of the internal heat exchanger of the embodiment. FIG. 4 is a sectional view taken along the X-X line in FIG. 3, and FIG. 5 is a sectional view taken along the Y-Y line in FIG. 3.

The internal heat exchanger 30 comprises a first heat exchanger tube 31 provided in the high pressure-side tube 15 extending from the radiator 12 to the expansion valve 13, and a second heat exchanger tube 32 provided in the low pressure-side tube 16 extending from the evaporator 14 to the compressor 11. Opposite ends of the internal heat exchanger 30 have connection tubes 33 each having a predetermined length. The first heat exchanger tube 31 is thinner than the second heat exchanger tube 32. The first heat exchanger tube 31 is disposed in the second heat exchanger tube 32. High pressure refrigerant in the supercritical region flows through the first heat exchanger tube 31, and low pressure refrigerant flows through the second heat exchanger tube 32. A direction of flow of refrigerant in the first heat exchanger tube 31 and a direction of flow of refrigerant in the second heat exchanger tube 32 are opposite from each other.

Straight tubes having smooth surfaces are used as the first heat exchanger tube 31 and the second heat exchanger tube 32, and they are formed with predetermined bent portions in accordance with spaces in which they are disposed. Especially as the first heat exchanger tube 31, a smooth tube whose outer surface is not provided with projections and depressions is preferable. It is preferable that only the first heat exchanger tube 31 is disposed in the second heat exchanger tube 32, and other member such as a supporting member of the first heat exchanger tube 31 on the second heat exchanger tube 32 is not provided. It is preferable that the cross-sectional area of the flow path for low pressure refrigerant formed by the first heat exchanger tube 31 and the second heat exchanger tube 32 is equal to or greater than a cross-sectional area of an inner diameter of the low pressure-side tube 16 which is an outlet-side tube of the evaporator 14.

Oil is deposited if flowing velocity of refrigerant is reduced. If this fact is taken into consideration, it is preferable that the cross-sectional area of the flow path of low pressure refrigerant formed by the first heat exchanger tube 31 and the second heat exchanger tube 32 is equal to or less than twice of cross-sectional area of the low pressure-side tube 16 which is the outlet-side tube of the evaporator 14.

A connection tube 33 has a predetermined length. One end side opening 33A of the connection tube 33 is formed smaller than the other end side opening 33B by diameter-increasing machining or diameter-reducing machining, the second heat exchanger tube 32 is connected to the one end side opening 33A by welding, and the first heat exchanger tube 31 and the low pressure-side tube 16 are connected to the other end side opening 33B by welding.

As in this embodiment, the first heat exchanger tube 31 is disposed in the second heat exchanger tube 32 and the low pressure refrigerant flows through the second heat exchanger tube 32. With this, as compared with a case in which low pressure refrigerant flows through the first heat exchanger tube 31, a contact area of the heat exchanger tube with the lubricating oil can be increased. Therefore, the film thickness of the lubricating oil on the outer surface of the first heat exchanger tube 31 can be reduced, and the heat exchanging efficiency in the internal heat exchanger is enhanced. More specifically, as shown in FIG. 2, if the temperature of CO₂ refrigerant in the internal heat exchanger is 10° C., CO₂ and oil are not separated into two phases and flow through the tube in the case of POE. In the case of PC, CO₂ and oil are separated into a refrigerant rich phase (oil rate is 7%) and an oil rich phase (oil rate is 22%) and flow through the tube and then, the amount of dissolved CO₂ is high also in the oil rich phase, a degree in which heat transfer is hindered by oil adhered to the tube is small. However, on the other hand, in the case of PAG#2, the CO₂ and oil are separated into refrigerant rich phase (oil rate is 0% refrigerant is 100%) and an oil rich phase (oil rate is 48%) and flow through the tube and thus, heat transfer is hindered by oil adhered to the tube. Therefore, when refractory oil is used, the above-described structure exhibits great effect.

As in this embodiment, the internal heat exchanger 30 is disposed in the compressor-side casing 10A, and is disposed at a location close to the compressor 11. With this structure, it is possible to prevent heat of refrigerant of the second heat exchanger tube 32 from being dissipated to the outside air. Therefore, since the suction temperature of the compressor 11 can be increased, the discharging temperature of the compressor 11 can be increased and the freezing efficiency can be enhanced. For example, if the inflow-side temperature of the first heat exchanger tube 31 is 20(C and the inflow-side temperature of the second heat exchanger tube 32 is 5(C, the outflow-side temperature of the first heat exchanger tube 31 is 15(C and the outflow-side temperature of the second heat exchanger tube 32 is about 10(C. In such a case, even when the outside air temperature is lower than 10(C, it is possible to prevent from the heat radiation from the second heat exchanger tube 32 only if the temperature in the compressor-side casing 10A is about 10(C by the heat of the compressor 11.

If the outer surface of the first heat exchanger tube 31 is smooth and other member such as a supporting member is not provided between the first heat exchanger tube 31 and the second heat exchanger tube 32 as in this embodiment, it is possible to smoothen the flow of lubricating oil and to reduce the remaining amount of lubricating oil in the internal heat exchanger.

As in this embodiment, the first heat exchanger tube 31 is connected to one of the openings 33B of the connection tube 33, the low pressure-side tube 16 is also connected to the opening 33B, high pressure refrigerant and low pressure refrigerant flow through the branch portion from the same opening 33B. With this, lubricating oil can smoothly flow through the inflow portion and outflow portion of the internal heat exchanger 30, the remaining amount of lubricating oil in the internal heat exchanger 30 can be reduced, and the heat exchanging efficiency in the internal heat exchanger can be enhanced.

As in this embodiment, the cross-sectional area of the flow path of the low pressure refrigerant formed by the first heat exchanger tube 31 and the second heat exchanger tube 32 is equal to or greater than the cross-sectional area of the inner diameter of the low pressure-side tube 16. With this, lubricating oil in the internal heat exchanger 30 can smoothly flow, the remaining amount of lubricating oil in the internal heat exchanger 30 can be reduced, and the heat exchanging efficiency in the internal heat exchanger can be enhanced.

SECOND EMBODIMENT

Next, an internal heat exchanger of another embodiment of the present invention will be explained.

FIG. 6 is a side view of an essential portion of the internal heat exchanger of the embodiment, and FIG. 7 is a sectional view taken along the line Z-Z in FIG. 6.

In the internal heat exchanger 30 of this embodiment, the first heat exchanger tube 31 comprises a plurality of first heat exchanger tubes 31A and 31B. If the first heat exchanger tube 31 comprises the plurality of first heat exchanger tubes 31A and 31B as in this embodiment, the contact area of the heat exchanger tube with respect to the lubricating oil can further be increased and thus, the film thickness of the lubricating oil in the outer surface of the first heat exchanger tubes 31A and 31B can further be reduced.

The two first heat exchanger tubes 31A and 31B are connected to the other end side opening 33B of the connection tube 33, and the low pressure-side tube 16 is connected in between the first heat exchanger tube 31A and the first heat exchanger tube 31B by welding.

Other structure of this embodiment is the same as that of the previous embodiment.

Although the refrigeration cycle apparatus 10 comprises the expansion valve 13, an expander may be used instead of the expansion valve 13.

Although the heat exchanger of refrigerant and water is used as the radiator 12 in the embodiment, it is also possible to use the same for a heat exchanger of refrigerant and refrigerant, and a heat exchanger of refrigerant and air.

INDUSTRIAL APPLICABILITY

The heat pump water heater of the invention is also suitable for a floor heater which requires high temperature water, and for an air conditioner or a drier as other apparatuses. 

1. A refrigeration cycle apparatus in which a compressor, a radiator, an expansion valve and an evaporator are connected to one another through tubes, said refrigeration cycle apparatus comprises an internal heat exchanger for exchanging heat between a high pressure refrigerant which flows out from said radiator and a low pressure refrigerant which flows out from said evaporator, wherein carbon dioxide is used as the refrigerant, refractory oil is used as lubricating oil in said compressor, said internal heat exchanger comprises a first heat exchanger tube through which the high pressure refrigerant in a supercritical region flows and a second heat exchanger tube through which the low pressure refrigerant flows, and said first heat exchanger tube is disposed in said second heat exchanger tube.
 2. The refrigeration cycle apparatus according to claim 1, wherein the number of first heat exchanger tube is two or more.
 3. The refrigeration cycle apparatus according to claim 1, wherein a straight tube having a smooth outer surface is used as said first heat exchanger tube, and only said first heat exchanger tube is disposed in said second heat exchanger tube.
 4. The refrigeration cycle apparatus according to claim 1, wherein said internal heat exchanger is provided at its opposite ends with connection tubes each having predetermined length, one end side opening of each of said connection tubes is formed smaller than the other end side opening by diameter-increasing machining or diameter-reducing machining, said second heat exchanger tube is connected to said one end side opening, said first heat exchanger tube is connected to said other end side opening, and a tube through which the low pressure refrigerant flows is connected to said other end side opening.
 5. The refrigeration cycle apparatus according to claim 1, wherein a flow path cross-sectional area of said low pressure refrigerant formed by said first heat exchanger tube and said second heat exchanger tube is equal to or greater than an inner diameter cross-sectional area of an outlet-side tube of said evaporator. 